Clip-style medical sensor and technique for using the same

ABSTRACT

A clip-style pulse sensor may be adapted to apply limited, even pressure to a patient&#39;s tissue. A clip-style sensor is provided that reduces motion artifacts by exerting limited, uniform pressure to the patient tissue to reduce tissue exsanguination. Further, such a sensor provides a secure fit while avoiding discomfort for the wearer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and, moreparticularly, to sensors used for sensing physiological parameters of apatient.

2. Description of the Related Art

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present inventionwhich are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of medicine, doctors often desire to monitor certainphysiological characteristics of their patients. Accordingly, a widevariety of devices have been developed for monitoring many suchphysiological characteristics. Such devices provide doctors and otherhealthcare personnel with the information they need to provide the bestpossible healthcare for their patients. As a result, such monitoringdevices have become an indispensable part of modem medicine.

One technique for monitoring certain physiological characteristics of apatient is commonly referred to as pulse oximetry, and the devices builtbased upon pulse oximetry techniques are commonly referred to as pulseoximeters. Pulse oximetry may be used to measure various blood flowcharacteristics, such as the blood-oxygen saturation of hemoglobin inarterial blood, the volume of individual blood pulsations supplying thetissue, and/or the rate of blood pulsations corresponding to eachheartbeat of a patient. In fact, the “pulse” in pulse oximetry refers tothe time varying amount of arterial blood in the tissue during eachcardiac cycle.

Pulse oximeters typically utilize a non-invasive sensor that transmitslight through a patient's tissue and that photoelectrically detects theabsorption and/or scattering of the transmitted light in such tissue.One or more of the above physiological characteristics may then becalculated based upon the amount of light absorbed or scattered. Morespecifically, the light passed through the tissue is typically selectedto be of one or more wavelengths that may be absorbed or scattered bythe blood in an amount correlative to the amount of the bloodconstituent present in the blood. The amount of light absorbed and/orscattered may then be used to estimate the amount of blood constituentin the tissue using various algorithms.

Conventional pulse oximetry sensors are either disposable or reusable.In many instances, it may be desirable to employ, for cost and/orconvenience, a reusable pulse oximeter sensor. Reusable sensors aretypically semi-rigid or rigid devices that may be clipped to a patient.Unfortunately, reusable sensors may be uncomfortable for the patient forvarious reasons. For example, sensors may have angled or protrudingsurfaces that, over time, may cause discomfort. In addition, reusablepulse oximeter sensors may pose other problems during use. For example,lack of a secure fit may allow light from the environment to reach thephotodetecting elements of the sensor, thus causing inaccuracies in theresulting measurement.

Because pulse oximetry readings depend on pulsation of blood through thetissue, any event that interferes with the ability of the sensor todetect that pulsation can cause variability in these measurements. Areusable sensor should fit snugly enough that incidental patient motionwill not dislodge or move the sensor, yet not so tight that normal bloodflow to the tissue is disrupted. As sensors are worn for several hoursat a time, an overly tight fit may cause local exsanguination of thetissue around the sensor. Exsanguinated tissue, which is devoid ofblood, shunts the sensor light through the tissue, resulting inincreased measurement errors.

SUMMARY

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms that the invention might take and that these aspectsare not intended to limit the scope of the invention. Indeed, theinvention may encompass a variety of aspects that may not be set forthbelow.

There is provided a sensor that includes: a sensor body having a firstportion and a second portion; a spring adapted to bias the first portiontowards the second portion; a stopping element adapted to establish aminimum distance between the first portion and the second portion; andat least one sensing element disposed on the sensor body.

There is provided a sensor that includes: a sensor body having a firstportion, a second portion; a spring adapted to bias the first portiontowards the second; a substrate disposed on at least one of the firstportion or the second portion, wherein the substrate is adapted to movewith at least one degree of freedom relative to the sensor body; and atleast one sensing element disposed on the substrate.

There is also provided a pulse oximetry system that includes: a pulseoximetry monitor and a pulse oximetry sensor adapted to be operativelycoupled to the monitor, the sensor comprising: a sensor body having afirst portion and a second portion; a spring adapted to bias the firstportion towards the second portion; a stopping element adapted toestablish a minimum distance between the first portion and the secondportion; and at least one sensing element disposed on the sensor body.

There is also provided a method of operating a sensor that includes:biasing a first portion and a second portion of a sensor body towardsone another with a spring; and establishing a minimum distance betweenthe first portion and the second portion with a stopper disposed on thesensor body.

There is also provided a method of manufacturing a sensor that includes:providing a sensor body having a first portion and a second portion;providing a spring adapted to bias the first portion towards the secondportion; providing a stopping element adapted to establish a minimumdistance between the first portion and the second portion; and providingat least one sensing element disposed on the sensor body.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1A illustrates a perspective view of an exemplary sensor with astopper and a flat spring according to the present invention;

FIG. 1B illustrates the sensor of FIG. 1A applied to a patient earlobeaccording to the present invention;

FIG. 2A illustrates a perspective view of an exemplary sensor with arigid bar according to the present invention;

FIG. 2B illustrates a cross-sectional view of the open sensor of FIG.2A;

FIG. 2C illustrates a cross-sectional view of the sensor of FIG. 2Aapplied to a patient's earlobe;

FIG. 3A illustrates a cross-sectional view of an open exemplary sensorwith a stopper within a hinge according to the present invention;

FIG. 3B illustrates a cross-sectional view of the sensor of FIG. 3Aapplied to a patient's earlobe;

FIG. 4A illustrates a cross sectional view of an exemplary sensor with astrap according to the present invention;

FIG. 4B illustrates a cross-sectional view of the sensor of FIG. 4Aapplied to a patient's earlobe;

FIG. 4C illustrates a cross sectional view of an alternative embodimentof the sensor of FIG. 4A with an offset emitter and detector;

FIG. 5A illustrates a cross sectional view of an exemplary sensor withpivoting heads according to the present invention.

FIG. 5B illustrates a cross-sectional view of the sensor of FIG. 5Aapplied to a patient's earlobe; and

FIG. 6 illustrates a pulse oximetry system coupled to a multi-parameterpatient monitor and a sensor according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

In accordance with the present technique, motion-resistant pulseoximetry sensors are provided that reduce measurement error by applyinglimited and uniform pressure to the optically probed tissue. Aclip-style sensor for pulse oximetry or other spectrophotometric uses isprovided that has a compliant material disposed on the sensor todistribute the spring force of the clip to the tissue evenly when thesensor is applied to a patient. The clip-style sensor may also have astopper that prevents the two portions of the clip from applying anexcess of pressure to the patient's tissue. Alternatively, theclip-style sensor may allow the light emitting and detecting componentsof the sensor to tilt or otherwise move to accommodate the patient'stissue and to prevent overly tight gripping at the sensor placementsite.

Pulse oximetry sensors are typically placed on a patient in a locationthat is normally perfused with arterial blood to facilitate measurementof the desired blood characteristics, such as arterial oxygen saturationmeasurement (SpO₂). The most common sensor sites include a patient'sfingertips, toes, earlobes, or forehead, and clip-style sensors are mostcommonly used on patient digits, earlobes, or nose bridges. Regardlessof the placement of the sensor 10, the reliability of the pulse oximetrymeasurement is related to the accurate detection of transmitted lightthat has passed through the perfused tissue. Hence, a sensor 10 thatfits a patient securely may reduce movement of the sensor and/orinfiltration of light from outside sources into the sensor, which maylead to more accurate pulse oximetry measurements.

There are several factors that may influence the tightness with which asensor may grip a patient's tissue. It is desirable to affix the sensor10 to the patient in a manner that does not exsanguinate the tissue, butthat provides sufficient pressure to squeeze out excess venous blood.Excess venous blood congestion in the optically probed tissue mayinfluence the relationship between the modulation ratio of thetime-varying light transmission signals of the wavelengths transmittedand SpO₂. As venous blood has an increased concentration ofdeoxyhemoglobin as compared to arterial blood, its contribution to thepulse oximetry measurement may shift the wavelength of the detectedlight. Thus, the pulse oximetry sensor may measure a mixedarterial-venous oxygen saturation and detect differences in signalmodulations unrelated to the underlying SpO₂ level. It is thereforedesirable to reduce the contribution of excess venous blood to the pulseoximetry measurement by clipping a sensor to a patient's tissue withenough spring force to squeeze out excess venous blood.

On the other hand, a patient's tissue may suffer if clipped too tightlyby a pulse oximetry sensor. In addition to causing patient discomfort, asensor with excess gripping force in a hinge spring or other closingmechanism may squeeze both arterial and venous blood from a patient'stissue, causing the tissue to become exsanguinated. Light from asensor's emitter that passes through such exsanguinated tissue may notbe modulated by arterial blood, which may cause the resulting SpO₂measurements to be artificially low. Thus, it is desirable to clip asensor 10 to a patient's tissue tightly enough to reduce the amount ofvenous blood congestion, but not so tightly as to interfere witharterial blood perfusion.

In accordance with the present techniques, examples of clip-stylesensors that apply limited, uniform pressure to a patient's tissue aredisclosed. An exemplary sensor 10A adapted for use on a patient'searlobe is illustrated in FIG. 1A. The sensor has a first portion 12 anda second portion 14 that are applied to opposite sides of an earlobe.The sensor body 16 includes a flat spring 18 that may be used to connectthe first portion 12 and the second portion 14. The first portion 12 andthe second portion 14 may have a rigid outer layer 20.

The sensor 10A may also include a stopper 22 that limits the distancethat the first portion 12 and the second portion 14 may move towards oneanother. Generally, it is envisioned that the stopper 22 be configuredto allow the first portion 12 to move towards the second portion 14 suchthat they are not able to move past a minimum distance from one anotherthat permits the sensor 10A to securely grip a patient's tissue. Such aminimum distance may generally be determined by the desired sensorplacement site (e.g. nose, earlobe, or digit) and the size of thepatient (e.g. child or adult). As the sensor 10A is applied to thepatient's earlobe 24, the stopper 22 absorbs part of the spring force ofthe flat spring 18 to prevent the sensor 10A from gripping the tissue sotightly as to cause exsanguinations or discomfort. The stopper 22 may bepermanently attached to the sensor body 16, or may be removable.

In an alternate embodiment, FIG. 2A depicts a perspective side view of asensor 10B with a permanently attached rigid bar 30 acting as a stopperbetween a first portion 32 and a second portion 34 of a sensor body 36.An emitter 26 is disposed on the first portion 32 and a detector 26 isdisposed on the second portion 34. The rigid bar 30 is permanentlyattached to the first portion 32 and moves away from the second portion34 during the opening of the sensor 10B, as shown in the cross-sectionalview of the open sensor 10B in FIG. 2B. However, it should be understoodthat the rigid bar 30 may alternatively be disposed on the secondportion 34 in other embodiments. The rigid bar 30 as depicted isdisposed on the first portion 32 of the sensor 10B in a region of thesensor body 36 that is free of intervening tissue when the sensor 10B isapplied an earlobe 38, as shown in FIG. 2C. As the sensor 10B is closed,the rigid bar 30 contacts the second portion 34 and prevents furtherbiasing of the first portion 32 towards the second portion 34. The firstportion 32 and the second portion 34 may be connected by a hinge 40 witha spring 42. Thus, the rigid bar 30 restricts the range of motion of thehinge 40, such that the hinge 40 may only move the first portion 32 andthe second portion 34 toward one another to a certain degree. Thus, themaximum spring force applied to the tissue is limited because the rigidbar 30 limits the force that the first portion 32 and the second portion34 may exert against the earlobe 38.

When the sensor 10B is applied to the patient's earlobe 38, as shown inFIG. 2C, a resilient pad 44 absorbs part of the force of the spring 42and distributes the remaining spring force to the earlobe 38 along thetissue-contacting surface of the sensor 10B. Thus, the total compressionresistance of the resilient material is generally less than the force ofthe spring 42. The resilient pad may be any shock-absorbing material,including foam, silicone, or rubber. The sensor 10B thereby evenlydistributes a limited force to the patient's tissue through use of aresilient pad 44, which spreads the force along the tissue-contactingsurface.

In an alternate embodiment, depicted in FIG. 2D, the sensor 10B mayinclude an adjustable bar 31 that may be threaded through an opening(not shown) in the sensor body 36. Thus, the length of the adjustablebar 31 may be increased by threading more length of the adjustable bar31 through the sensor body 36. In such an embodiment, the minimumdistance between the first portion 32 and the second portion 34 may beincreased to accommodate the tissue of larger patients. Alternatively,smaller patients may require adjustment of the adjustable bar 31 suchthat more of the adjustable bar is threaded outside the sensor body 36(i.e. not in the region between the first portion 32 and the secondportion 34). Additionally, the sensor 10B may be applied to the patient,and a healthcare worker may adjust the length of the adjustable bar 31until a desired amount of pressure on the tissue is achieved. In certainembodiments, the adjustable bar may be further secured by a nut 33 orother holding mechanism.

It is also envisioned that spring force of a hinge may be restricted byother mechanical structures. For example, in an alternative embodimentshown in FIG. 3A and FIG. 3B, a sensor 10C has a stopper 46 that isdisposed within the mechanism of a hinge 48 to restrict rotationalmotion, thus preventing the hinge 48 from exerting maximum pressure tothe tissue when sensor 10C is applied to a patient's earlobe 58. Thestopper 46 may be a rigid material that is designed to mechanicallyblock the motion of the hinge 48.

As depicted, the emitter 50 and the detector 52 are disposed on a thinsubstrate 54. The substrate 54 may be any suitable material, includingplastic or woven cloth, and may be rigid or flexible. The substrate 54may be disposed on the tissue-contacting side of a resilient pad 56. Incertain embodiments, it may be advantageous to employ a flexiblesubstrate 54, which may conform more closely to a patient's tissue whenthe sensor 10C is applied. In other embodiments, a more rigid substrate54 may absorb more of the spring force of the hinge 48, and thus mayprevent the sensor 10K from exerting excess pressure on the tissue.

Alternatively, as shown by the embodiment illustrated in FIGS. 4A-D, asensor 10D may have a flexible but inelastic strap 60, such as a plasticor metal strap, disposed on the handle end 62 of the sensor body,connecting the first portion 64 and the second portion 66. When thesensor 10D is open, the strap 60 is slack. When the sensor 10D isclosed, such as when the sensor 10D is applied to a patient, as shown inFIG. 4B, the strap 60 is drawn taut, thus preventing the hinge 68 frommoving the first portion 64 and the second portion 66 closer than adistance dictated by the length of the strap 60.

As depicted, the sensor 10D has resilient pads 70 disposed on thetissue-contacting sides of the first portion 64 and the second portion66 of a sensor. The use of a resilient pad 70 on both the first portion64 and the second portion 66 provides greater compression resistanceagainst the spring force of the hinge 68 than only a single resilientpad. Additionally, the spring force is evenly distributed along thetissue-contacting surface that holds both the emitter 72 and thedetector 74 against the tissue. Thus, a sensor 10D may be used inconjunction with a relatively strong spring. This may be advantageous insituations in which an ambulatory patient may require the sensor 10D tofit securely enough to withstand dislodgement in response to everydayactivity.

In an alternate embodiment, FIG. 4C illustrates a sensor 10D with anadjustable strap 61. The adjustable strap 61 may be threaded through anopening (not shown) in the sensor body. When an appropriate length ofthe adjustable strap is disposed between the first portion 64 and thesecond portion 66 to provide the desired pressure on a patient's tissue,the adjustable strap 61 may be held in place by a clamp 63. As morelength of the adjustable strap 61 is released into the region betweenthe first portion 64 and the second portion 66, the sensor 10D is ableto close more tightly over the tissue. Alternatively, a healthcareworker may pull the adjustable strap 61 through the sensor body suchthat the length of adjustable strap 61 between the first portion 64 andthe second portion 66 is decreased, and as a result the sensor 10D wouldexert less pressure on the tissue.

Clip-style sensors as provided herein are often used on a patient'searlobes, which may have fewer vascular structures as compared to adigit. To maximize the transmission of light through well-perfusedcapillary structures, an alternative embodiment of the sensor 10D isdepicted in which the emitter 72 and detector 74 are offset from eachother, so that they are not directly opposite. This causes the lightemitted by the emitter 72 to pass through more blood-perfused tissue toreach the detector 74. As such, the light has a greater opportunity tobe modulated by arterial blood in a manner which relates to a bloodconstituent. FIG. 4D illustrates that the configuration of the sensor10D provides a longer light transmission path through the tissue, asindicated by arrow 75.

FIG. 5A and FIG. 5B depict an embodiment of a sensor 10E in which partof the spring force of a hinge 76 is absorbed by pivoting heads 78, uponwhich an emitter 80 and a detector 82 are disposed. The pivoting heads78 are disposed on a first portion 84 and a second portion 86 of thesensor 10E. The first portion 84 and the second portion 86 are connectedby the hinge 76. Pivoting heads are disposed on the tissue-contactingside of the first portion 84 and the second portion 86. As FIG. 5Billustrates, the pivoting heads 78 may tilt relative to the sensor body88 in order to accommodate the contours of the patient's tissue. Incertain embodiments, the pivoting heads 78 may also include resilientpads (not shown) that distribute the spring force of the hinge 76 alongthe tissue-contacting surface of the sensor 10E. In other embodiments,the sensor 10E may also include a stopper or stopping mechanism asdescribed herein.

In an alternate embodiment (not shown), an adhesive material is appliedto the tissue-contacting surface of the sensor 10 to enhance thesecuring of the sensor 10 to the tissue. The use of an adhesive materialmay improve the contact of the sensor to the appendage, and limit thesusceptibility to motion artifacts. In addition, the likelihood of a gapbetween the sensor body and the skin is avoided.

In certain embodiments, it is contemplated that the spring force of thehinge (e.g. 40, 48, 68, or 78) or other closing mechanism, such as aflat spring (e.g. flat spring 18), has sufficient pressure so that itexceeds the typical venous pressure of a patient, but does not exceedthe diastolic arterial pressure. A sensor 10 that applies a pressuregreater than the venous pressure will squeeze excess venous blood fromthe optically probed tissue, thus enhancing the sensitivity of thesensor to variations in the arterial blood signal. Since the pressureapplied by the sensor is designed to be less than the arterial pressure,the application of pressure to the tissue does not interfere with thearterial pulse signal. Typical venous pressure, diastolic arterialpressure and systolic arterial pressure are less than 10-35 mmHg, 80mmHg, and 120 mmHg, respectively. These pressures may vary because ofthe location of the vascular bed and the patient's condition. In certainembodiments, the sensor may be adjusted to overcome an average pressureof 15-30 mmHg. In other embodiments, low arterial diastolic bloodpressure (about 30 mmHg) may occur in sick patients. In suchembodiments, the sensor 10 may remove most of the venous pooling withlight to moderate pressure (to overcome about 15 mmHg). It iscontemplated that removing venous blood contribution without arterialblood exsanguination may improve the arterial pulse signal.

The exemplary sensors described above, illustrated generically as asensor 10, may be used in conjunction with a pulse oximetry monitor 90,as illustrated in FIG. 6. It should be appreciated that the cable 92 ofthe sensor 10 may be coupled to the monitor 90 or it may be coupled to atransmission device (not shown) to facilitate wireless transmissionbetween the sensor 10 and the monitor 90. The monitor 90 may be anysuitable pulse oximeter, such as those available from Nellcor PuritanBennett Inc. Furthermore, to upgrade conventional pulse oximetryprovided by the monitor 90 to provide additional functions, the monitor90 may be coupled to a multi-parameter patient monitor 94 via a cable 96connected to a sensor input port or via a cable 98 connected to adigital communication port.

The sensor 10 includes an emitter 100 and a detector 102 that may be ofany suitable type. For example, the emitter 100 may be one or more lightemitting diodes adapted to transmit one or more wavelengths of light inthe red to infrared range, and the detector 102 may be a photodetectorselected to receive light in the range or ranges emitted from theemitter 100. For pulse oximetry applications using either transmissionor reflectance type sensors, the oxygen saturation of the patient'sarterial blood may be determined using two or more wavelengths of light,most commonly red and near infrared wavelengths. Similarly, in otherapplications, a tissue water fraction (or other body fluid relatedmetric) or a concentration of one or more biochemical components in anaqueous environment may be measured using two or more wavelengths oflight, most commonly near infrared wavelengths between about 1,000 nm toabout 2,500 nm. It should be understood that, as used herein, the term“light” may refer to one or more of infrared, visible, ultraviolet, oreven X-ray electromagnetic radiation, and may also include anywavelength within the infrared, visible, ultraviolet, or X-ray spectra.

The emitter 100 and the detector 102 may be disposed on a sensor body104, which may be made of any suitable material, such as plastic, foam,woven material, or paper. Alternatively, the emitter 100 and thedetector 102 may be remotely located and optically coupled to the sensor10 using optical fibers. In the depicted embodiments, the sensor 10 iscoupled to a cable 92 that is responsible for transmitting electricaland/or optical signals to and from the emitter 100 and detector 102 ofthe sensor 10. The cable 92 may be permanently coupled to the sensor 10,or it may be removably coupled to the sensor 10—the latter alternativebeing more useful and cost efficient in situations where the sensor 10is disposable.

The sensor 10 may be a “transmission type” sensor. Transmission typesensors include an emitter 100 and detector 102 that are typicallyplaced on opposing sides of the sensor site. If the sensor site is afingertip, for example, the sensor 10 is positioned over the patient'sfingertip such that the emitter 100 and detector 102 lie on either sideof the patient's nail bed. In other words, the sensor 10 is positionedso that the emitter 100 is located on the patient's fingernail and thedetector 102 is located 180° opposite the emitter 100 on the patient'sfinger pad. During operation, the emitter 100 shines one or morewavelengths of light through the patient's fingertip and the lightreceived by the detector 102 is processed to determine variousphysiological characteristics of the patient. In each of the embodimentsdiscussed herein, it should be understood that the locations of theemitter 100 and the detector 102 may be exchanged. For example, thedetector 102 may be located at the top of the finger and the emitter 100may be located underneath the finger. In either arrangement, the sensor10 will perform in substantially the same manner.

Reflectance type sensors generally operate under the same generalprinciples as transmittance type sensors. However, reflectance typesensors include an emitter 100 and detector 102 that are typicallyplaced on the same side of the sensor site. For example, a reflectancetype sensor may be placed on a patient's fingertip or forehead such thatthe emitter 100 and detector 102 lie side-by-side. Reflectance typesensors detect light photons that are scattered back to the detector102.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Indeed, the presenttechniques may not only be applied to measurements of blood oxygensaturation, but these techniques may also be utilized for themeasurement and/or analysis of other blood constituents using principlesof pulse oximetry. Rather, the invention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the following appended claims.

1. A sensor adapted to be applied to a patient's tissue comprising: asensor body having a first portion and a second portion; a springadapted to bias the first portion towards the second portion; a stoppingelement adapted to establish a minimum distance between the firstportion and the second portion; and at least one sensing elementdisposed on the sensor body.
 2. The sensor, as set forth in claim 1,comprising a resilient material disposed on at least one of the firstportion or the second portion.
 3. The sensor, as set forth in claim 2,wherein the spring is adapted to apply a spring force at least greaterthan a compression resistance of the resilient material.
 4. The sensor,as set forth in claim 1, wherein the stopping element comprises a rigidbar.
 5. The sensor, as set forth in claim 1, wherein the stoppingelement comprises a plug.
 6. The sensor, as set forth in claim 1,wherein the stopping element comprises a substantially inelastic strap.7. The sensor, as set forth in claim 1, wherein the sensor is adapted toapply a spring force to the patient's tissue adapted to overcome a bloodpressure of about 35 mm Hg or less.
 8. The sensor, as set forth in claim1, wherein the resilient material comprises a foam.
 9. The sensor, asset forth in claim 1, wherein the emitter and the detector are disposedon a flexible substrate disposed on a tissue-contacting side of theresilient material.
 10. The sensor, as set forth in claim 1, comprisingan adhesive material disposed on at least one of a tissue-contactingsurface of the first portion or a tissue-contacting surface of thesecond portion.
 11. The sensor, as set forth in claim 1, wherein thesensing element comprises an emitter and a detector.
 12. The sensor, asset forth in claim 1 1, wherein the emitter comprises a light-emittingdiode and the detector comprises a photodetector.
 13. The sensor, as setforth in claim 11, wherein the emitter is disposed on the first portionand the detector is disposed on the second portion such that the emitterand the detector are not opposite each other.
 14. The sensor, as setforth in claim 1, wherein the sensor comprises at least one of a pulseoximetry sensor, a sensor for measuring a water fraction, or acombination thereof.
 15. The sensor, as set forth in claim 1, comprisingat least one integrated circuit device.
 16. The sensor, as set forth inclaim 1, comprising a cable comprising one or more integrated circuits.17. The sensor, as set forth in claim 1, comprising an adapter cableconnected to one or more signal transmission structures of the sensorassembly.
 18. A pulse oximetry system comprising: a pulse oximetrymonitor; and a pulse oximetry sensor adapted to be operatively coupledto the monitor, the sensor comprising: a sensor body having a firstportion and a second portion; a spring adapted to bias the first portiontowards the second portion; a stopping element adapted to establish aminimum distance between the first portion and the second portion; andat least one sensing element disposed on the sensor body.
 19. The pulseoximetry system, as set forth in claim 18, comprising a resilientmaterial disposed on at least one of the first portion or the secondportion.
 20. The pulse oximetry system, as set forth in claim 19,wherein the spring is adapted to apply a spring force at least greaterthan a compression resistance of the resilient material.
 21. The pulseoximetry system, as set forth in claim 18, wherein the stopping elementcomprises a rigid bar.
 22. The pulse oximetry system, as set forth inclaim 18, wherein the stopping element comprises a plug.
 23. The pulseoximetry system, as set forth in claim 18, wherein the stopping elementcomprises a substantially inelastic strap.
 24. The pulse oximetrysystem, as set forth in claim 18, wherein the sensor is adapted to applya spring force to the patient's tissue adapted to overcome a bloodpressure of about 35 mm Hg or less.
 25. The pulse oximetry system, asset forth in claim 18, wherein the resilient material comprises a foam.26. The pulse oximetry system, as set forth in claim 18, wherein theemitter and the detector are disposed on a flexible substrate disposedon a tissue-contacting side of the resilient material.
 27. The pulseoximetry system, as set forth in claim 18, comprising an adhesivematerial disposed on at least one of a tissue-contacting surface of thefirst portion or a tissue-contacting surface of the second portion. 28.The pulse oximetry system, as set forth in claim 18, wherein the sensingelement comprises an emitter and a detector.
 29. The pulse oximetrysystem, as set forth in claim 28, wherein the emitter comprises alight-emitting diode and the detector comprises a photodetector.
 30. Thepulse oximetry system, as set forth in claim 28, wherein the emitter isdisposed on the first portion and the detector is disposed on the secondportion such that the emitter and the detector are not opposite eachother.
 31. The pulse oximetry system, as set forth in claim 18, whereinthe sensor further comprises a sensor for measuring a water fraction.32. The pulse oximetry system, as set forth in claim 18, comprising atleast one integrated circuit device.
 33. The pulse oximetry system, asset forth in claim 18, comprising a cable comprising one or moreintegrated circuits.
 34. The pulse oximetry system, as set forth inclaim 18, comprising an adapter cable connected to one or more signaltransmission structures of the sensor assembly.
 35. A method comprising:biasing a first portion and a second portion of a sensor body towardsone another with a spring; and establishing a minimum distance betweenthe first portion and the second portion with a stopper disposed on thesensor body;
 36. The method, as set forth in claim 35, comprisingabsorbing part of a spring force of the hinge with a rigid bar.
 37. Themethod, as set forth in claim 35, comprising absorbing part of a springforce of the hinge with an inelastic strap.
 38. The method, as set forthin claim 35, comprising absorbing part of a spring force of the hingewith a plug.
 39. A method of manufacturing a sensor, comprising:providing a sensor body having a first portion and a second portion;providing a spring adapted to bias the first portion towards the secondportion; providing a stopping element adapted to establish a minimumdistance between the first portion and the second portion; and providingat least one sensing element disposed on the sensor body.
 40. Themethod, as set forth in claim 39, comprising a resilient materialdisposed on at least one of the first portion or the second portion. 41.The method, as set forth in claim 40, wherein the spring is adapted toapply a spring force at least greater than a compression resistance ofthe resilient material.
 42. The method, as set forth in claim 39,wherein the stopping element comprises a rigid bar.
 43. The method, asset forth in claim 39, wherein the stopping element comprises a plug.44. The method, as set forth in claim 39, wherein the stopping elementcomprises a substantially inelastic strap.
 45. The method, as set forthin claim 39, wherein the resilient material comprises a foam.
 46. Themethod, as set forth in claim 39, comprising: providing a flexiblesubstrate disposed on a tissue-contacting side of the resilientmaterial.
 47. The method, as set forth in claim 39, comprising:providing an adhesive material disposed on at least one of atissue-contacting surface of the first portion or a tissue-contactingsurface of the second portion.
 48. A sensor adapted to be applied to apatient's tissue comprising: a sensor body having a first portion, asecond portion; a spring adapted to bias the first portion towards thesecond; a substrate disposed on at least one of the first portion or thesecond portion, wherein the substrate is adapted to move with at leastone degree of freedom relative to the sensor body; and at least onesensing element disposed on the substrate.
 49. The sensor, as set forthin claim 48, wherein the substrate is adapted to pivot on a pin disposedon the first portion or the second portion.
 50. The sensor, as set forthin claim 48, wherein the substrate is connected to the first portion orthe second portion by a hinge.
 51. The sensor, as set forth in claim 48,wherein the sensor is adapted to apply a spring force to the patient'stissue adapted to overcome a blood pressure of about 35 mm Hg or less.52. The sensor, as set forth in claim 48, further comprising a resilientmaterial disposed on at least one of the first portion or the secondportion.
 53. The sensor, as set forth in claim 52, wherein a resilientmaterial is disposed on the substrate.
 54. The sensor, as set forth inclaim 52, wherein the resilient material comprises a foam.
 55. Thesensor, as set forth in claim 48, comprising an adhesive materialdisposed on at least one of a tissue-contacting surface of the firstportion or a tissue-contacting surface of the second portion.
 56. Thesensor, as set forth in claim 48, wherein the sensing element comprisesan emitter and a detector.
 57. The sensor, as set forth in claim 56,wherein the emitter comprises a light-emitting diode and the detectorcomprises a photedetector.
 58. The sensor, as set forth in claim 56,wherein the emitter is disposed on the first portion and the detector isdisposed on the second portion such that the emitter and the detectorare not opposite each other.
 59. The sensor, as set forth in claim 48,wherein the sensor comprises at least one of a pulse oximetry sensor, asensor for measuring a water fraction, or a combination thereof.
 60. Thesensor, as set forth in claim 48, comprising at least one integratedcircuit device.
 61. The sensor, as set forth in claim 48, comprising acable comprising one or more integrated circuits.